This grower is sure of this plant identification.
a miniature version of evening primrose.
Evening primrose, Sun drops, Sun cups
Oenothera genus (Evening primrose). This genus consists of about 120 species of annuals, biennials and perennials. They will produce short-lived flowers which are borne during the summer, with 4 delicate petals which can be yellow or sometimes pink, red or white.
They usually frost hardy and will grow best in a well-drained, sandy soil in an open, sunny situation, and they will tolerate dry conditions. You can propagate from seeds or by division in spring or autumn, or from softwood cuttings in late spring.
Grown for their profuse but short-lived flowers in summer. Suitable for coastal conditions. Oenothera biennis is used medicinally.